Fringe scanning digital interferometer was first proposed by J. H. Burning et al of Bell Telephone Company of United States in 1974 (Appl. Opt. 1974, Vol 13, No.11. P2693), and then was commercialized by TROPEL Company and ZYGO company (M. Sohaham SPIE, 1981, Vol 306 183; U.S. Pat. No. 4,201,473). Today it has become the most effective tool for high accuracy wavefront measurements.
In the fringe scanning digital interferometer of the prior art, for example, ZYGO interferometer, it comprises light source, fringe scanning interference unit, photoelectric measurement means and data processing system, where the fringe scanning is carried out by varying the distance passed by one interference beam using piezoelectric crystal. However, this method has following disadvantages:
1. It is hard to control the piezoelectric crystal with high precision;
2. A two beam interference means must be employed, in which the measurement system is very sensitive to turbulence and external vibrations, so a very critical environment, where the measurement is carried out, is required;
3. A high accuracy reference wavefront is needed. It also requires other high quality optical components;
4. The light source must be a frequency-stabilized laser;
5. The interference fringes are unstable, so it is hard to observe the zeroth-order interference fringe of aberration;
6. The apparatus has a complicated structure.
To eliminate above disadvantages, the inventor of the present invention proposed a new kind of fringe scanning principle, polarization fringe scanning, in the 13th international conference on optics in Japan, August, 1984, and submitted an article of "Polarization Fringe Scanning Interferometer" to "Acta Optica Sinica" to make a further exposition of the polarization fringe scanning principle (Acta Optica Sinica, 1985. Vol. 5, No. 2).